The present invention relates generally to sealing a centrifuge tube within a centrifuge rotor and, more particularly, is related to sealing arrangements used for sealing the rotor tube cavity in which the centrifuge tube resides.
Analytical and comparative centrifuges are commonly provided with a rotor having a series of cavities which are arranged in a generally circular orientation for receipt of centrifuge tubes carrying a sample to be centrifugated. In many prior art rotor cavity arrangements the axis of each cavity is annularly oriented with respect to the vertical rotational axis of the rotor, so that the bottom of the centrifuge tube is further away from the rotor axis than the top of the tube. An example of such an annuarly oriented rotor cavity rotor is shown in FIG. 5 of U.S. Pat. No. 2,878,992 issued to Pickels et al. on Mar. 24, 1959 and assigned to the assignee of the present invention.
During centrifugation the sample, which is initially in the lower end of the centrifuge tube, attains a somewhat vertical orientation which is essentially parallel to the rotational axis. Because the orientation of the test tube and the rotor, a portion of the sample reaches the upper end of the test tube and exerts a significant amount of loading on the capping arrangement at the upper end of the test tube. Consequently, because of the high G forces experienced by the test tube capping arrangement, it is extremely important to design a sealing arrangement on the centrifuge tube to retain the fluid sample within the centrifuge tube and reduce the possibility of escape of the fluid from the rotor which may cause a serious imbalance in the rotor, resulting in serious damage not only to the rotor but to the drive system.
Many approaches have been used to provide the necessary sealing of the upper end of the centrifuge tube in order to ensure the retention of the fluid sample within the tube during high speed centrifugation. An exemplary solution is shown in the U.S. Pat. No. 3,938,735 patent issued to Wright et al. on Feb. 17, 1976 and the U.S. Pat. No. 3,447,712 issued to M. Galasso on June 3, 1969. Both of these patents are directed to approaches for tightly sealing the upper end of the centrifuge tube to inhibit any escape of the fluid sample.
Recently, however, rotors have been designed which incorporate a series of vertical tube cavities oriented in a circular fashion around the rotational axis of the rotor. In such a configuration, the cavities are essentially parallel to the rotational axis of the rotor. The sealing of the centrifuge tube sample within the tube itself as well as within the rotor becomes extremely critical, because even a greater amount of the fluid sample will be exerting higher centrifugally induced forces on the upper end of the test tube during centrifugation than in the case of fixed angle tube rotors where the top of the test tube or centrifuge tube is closer to the rotational axis than the bottom of the tube. Since centrifuge tubes are typically made of a thin flexible material, there may be a week point which under high G loading exerted by the fluid could result in possible tube leakage, allowing the fluid to escape out of the rotor and resulting in possible damage to the rotor. Also, it is important with respect to certain biological samples, that it reduces the possibility of the sample escaping from the rotor.
One recent development in the area of vertical tube rotors has been the design of an essentially completely enclosed centrifuge tube which does not require any special or separate capping arrangement, but rather has a small fill port which is later heat sealed with integral material to provide essentially a completely enclosed tube without the use of another type of material to provide a capping arrangement. Reference is made to a copending application entitled INTEGRAL ONE PIECE CENTRIFUGE TUBE, Ser. No. 912,698, filed June 5, 1978 by Steven T. Nielsen. In any event, although a special capping arrangement is not necessary for the centrifuge tube itself, it is still important that a secondary sealing arrangement be devised to reduce the possibility of escape of the fluid sample from the rotor in the event that some defect in the tube should result in a leakage of the fluid out of the tube.
Some prior art approaches have been suggested for the creation of a secondary seal as shown in U.S. Pat. No. 4,087,043, using a channel like ring member which is designed to snap into a position around the edge of the crown member on the capping arrangement for attachment to an open ended centrifuge tube. Although this approach provides a secondary seal, its construction in conjunction with the centrifuge tube capping arrangement provides a fairly unique and distinct type of approach which is conducive to such an arrangement with the use of a capping arrangement having a crown member with a particular rim or outer edge configuration. With the use of newly designed completely enclosed centrifuge tubes the need for a separate capping arrangement with a crown member is eliminated and, therefore, a requirement exists for the use of a secondary sealing arrangement which can be constructed and utilized independent of a tube capping arrangement.